This invention relates to a vehicle traction control system and, more particularly, to such a system which limits driven wheel torque input for limiting acceleration wheel slip.
It is a common experience with automotive vehicles for excessive wheel slip to occur during vehicle acceleration when the operator initiated engine torque delivered to the vehicle driven wheels are such that the frictional forces between the tire and the road surface are overcome. While a small amount of slip between the tire and road surface is necessary in order to achieve a driving force, excessive slip results in the reduction of effective driving force and in the deterioration in the lateral stability of the vehicle.
Various methods have been proposed for preventing an excessive slip condition of the driven wheels of a vehicle by limiting the slip between the wheel and the road surface at a value that will achieve a maximum transfer of driving force from the driven wheels to the road surface. For example, in one method, the output power of the engine is reduced by reducing the amount of fuel delivered to the engine when an excessive slip condition is detected.
Another method of limiting the acceleration slip of the driven wheels controls the throttle valve regulating the air intake of the engine to limit engine output torque to the driven wheels. In this form of system, it is typical to ramp the throttle closed in response to a sensed excessive slip condition and ramp the throttle open in response to a sensed recovery from the excessive slip condition.
In whichever form of controller employed, it is desirable to prevent large excursions of wheel slip which tend to reduce the driving force and lateral vehicle stability and to control wheel slip to a desired level to establish an optimum vehicle propulsion. It is further desirable to provide for such control that is stable under all vehicle accelerating conditions.